From: Chen Yu <yu.c.chen@intel.com>
To: Honglei Wang <wanghonglei@didichuxing.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Tim Chen <tim.c.chen@intel.com>,
Mel Gorman <mgorman@techsingularity.net>,
Juri Lelli <juri.lelli@redhat.com>,
"Rik van Riel" <riel@surriel.com>, Aaron Lu <aaron.lu@intel.com>,
Abel Wu <wuyun.abel@bytedance.com>,
K Prateek Nayak <kprateek.nayak@amd.com>,
"Yicong Yang" <yangyicong@hisilicon.com>,
"Gautham R . Shenoy" <gautham.shenoy@amd.com>,
Ingo Molnar <mingo@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Valentin Schneider <vschneid@redhat.com>,
Hillf Danton <hdanton@sina.com>, Len Brown <len.brown@intel.com>,
Chen Yu <yu.chen.surf@gmail.com>,
"Tianchen Ding" <dtcccc@linux.alibaba.com>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Don <joshdon@google.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 1/2] sched/fair: Introduce short duration task check
Date: Sat, 3 Dec 2022 15:49:30 +0800 [thread overview]
Message-ID: <Y4r/iuqyLG4MOK4d@chenyu5-mobl1> (raw)
In-Reply-To: <8d976d4a-ecb6-41af-85b0-65e6022a0d82@didichuxing.com>
Hi Honglei,
On 2022-12-02 at 15:44:18 +0800, Honglei Wang wrote:
>
>
> On 2022/12/1 16:44, Chen Yu wrote:
> > Introduce short-duration task checks, as there is requirement
> > to leverage this attribute for better task placement.
> >
> > There are several choices of metrics that could be used to
> > indicate if a task is a short-duration task.
> >
> > At first thought the (p->se.sum_exec_runtime / p->nvcsw)
> > could be used to measure the task duration. However, the
> > history long past was factored too heavily in such a formula.
> > Ideally, the old activity should decay and not affect
> > the current status too much.
> >
> > Although something based on PELT could be used, se.util_avg might
> > not be appropriate to describe the task duration:
> > 1. Task p1 and task p2 are doing frequent ping-pong scheduling on
> > one CPU, both p1 and p2 have a short duration, but the util_avg
> > can be up to 50%.
> > 2. Suppose a task lasting less than 4ms is regarded as a short task.
> > If task p3 runs for 6ms and sleeps for 32ms, p3 should not be a
> > short-duration task. However, PELT would decay p3's accumulated
> > running time from 6ms to 3ms, because 32ms is the half-life in PELT.
> > As a result, p3 would be incorrectly treated as a short task.
> >
> > It was found that there was once a similar feature to track the
> > duration of a task, which is in Commit ad4b78bbcbab ("sched: Add
> > new wakeup preemption mode: WAKEUP_RUNNING"). Unfortunately, it
> > was reverted because it was an experiment. So pick the patch up
> > again, by recording the average duration when a task voluntarily
> > switches out. Introduce SIS_SHORT to control this strategy.
> >
> > The threshold of short duration reuses sysctl_sched_min_granularity,
> > so it can be tuned by the user. Ideally there should be a dedicated
> > parameter for the threshold, but that might introduce complexity.
> >
> > Suggested-by: Tim Chen <tim.c.chen@intel.com>
> > Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
> > Signed-off-by: Chen Yu <yu.c.chen@intel.com>
> > ---
> > include/linux/sched.h | 4 ++++
> > kernel/sched/core.c | 2 ++
> > kernel/sched/fair.c | 17 +++++++++++++++++
> > kernel/sched/features.h | 1 +
> > 4 files changed, 24 insertions(+)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index ffb6eb55cd13..64b7acb77a11 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -558,6 +558,10 @@ struct sched_entity {
> > u64 nr_migrations;
> > + u64 prev_sum_exec_runtime_vol;
> > + /* average duration of a task */
> > + u64 dur_avg;
> > +
> > #ifdef CONFIG_FAIR_GROUP_SCHED
> > int depth;
> > struct sched_entity *parent;
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index daff72f00385..c5202f1be3f7 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -4348,6 +4348,8 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
> > p->se.prev_sum_exec_runtime = 0;
> > p->se.nr_migrations = 0;
> > p->se.vruntime = 0;
> > + p->se.dur_avg = 0;
> > + p->se.prev_sum_exec_runtime_vol = 0;
> > INIT_LIST_HEAD(&p->se.group_node);
> > #ifdef CONFIG_FAIR_GROUP_SCHED
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index e4a0b8bd941c..a4b314b664f8 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6200,6 +6200,16 @@ static int wake_wide(struct task_struct *p)
> > return 1;
> > }
> > +/*
> > + * If a task switches in and then voluntarily relinquishes the
> > + * CPU quickly, it is regarded as a short duration task.
> > + */
> > +static inline int is_short_task(struct task_struct *p)
> > +{
> > + return sched_feat(SIS_SHORT) &&
> > + (p->se.dur_avg <= sysctl_sched_min_granularity);
> > +}
> > +
>
> Hi Yu,
>
> I still have a bit concern about the sysctl_sched_min_granularity stuff..
> This grab can be set to different value which will impact the action of this
> patch and make things not totally under control.
>
> Not sure if we can add a new grab for this.. The test result shows good
> improvement for short task, and with this grab, admins will be able to
> custom the system base on their own 'short task' view.
>
It would be ideal to have a dedicated parameter to tweak this. For example,
something under /sys/kernel/debug/sched/, and initilized to sysctl_sched_min_granularity
by default.
Hi Peter, Vincent,
may I have your opinion if this is applicable?
thanks,
Chenyu
next prev parent reply other threads:[~2022-12-03 7:50 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-01 8:43 [PATCH v3 0/2] sched/fair: Choose the CPU where short task is running during wake up Chen Yu
2022-12-01 8:44 ` [PATCH v3 1/2] sched/fair: Introduce short duration task check Chen Yu
2022-12-02 7:44 ` Honglei Wang
2022-12-03 7:49 ` Chen Yu [this message]
2022-12-03 15:35 ` Joel Fernandes
2022-12-05 8:38 ` Chen Yu
2022-12-05 9:59 ` Vincent Guittot
2022-12-05 14:38 ` Chen Yu
2022-12-07 2:23 ` Josh Don
2022-12-07 14:24 ` Chen Yu
2022-12-12 11:22 ` Yicong Yang
2022-12-12 14:33 ` Chen Yu
2022-12-12 18:17 ` Josh Don
2022-12-13 5:46 ` Chen Yu
2022-12-13 10:06 ` Honglei Wang
2022-12-13 12:24 ` Chen Yu
2022-12-01 8:44 ` [PATCH v3 2/2] sched/fair: Choose the CPU where short task is running during wake up Chen Yu
2022-12-05 2:36 ` Tianchen Ding
2022-12-05 8:40 ` Chen Yu
2022-12-06 13:02 ` Yicong Yang
2022-12-07 3:54 ` Chen Yu
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